Trichogramma

 ( Trichogrammatidae ) 

Transmission of the bacterium through horizontal transfer has been observed within the same species and among different species of Trichogramma, including T. kaykai, T. deion, T. pretiosum, and T. atopovirilia; however, limitations to transmission exist. In vitro successful horizontal transfer is uncommon within Trichogramma, which suggests that the density of Wolbachia must be relatively high inside of the hosts' ovaries. Cytoplasmic incompatibility of the host and bacterium can also be the source of this unsuccessful transfer in-vitro. These limitations in vitro suggest that in nature, horizontal transfer by parthenogenesis-inducing Wolbachia may be a difficult and rare phenomenon. However, when looking at the Wolbachia-host associations, the Trichogramma-Wolbachia form a monophyletic group based on several Wolbachia-specific genes, which may be explained by horizontal transfer of Wolbachia between different species. Therefore, although interspecific horizontal transfer of Wolbachia is limited in vitro, it is likely to occur quite frequently in nature and is not well understood yet.

The effects of Wolbachia in Trichogramma have several evolutionary implications. Commonly, uninfected wasps are unable to breed with infected wasps. Many generations of reproductive isolation of these different groups may result in speciation. In addition, some hosts can evolve with a dependency on Wolbachia for core reproductive functions, such as oogenesis, so that eventually an infection is a requirement for successful reproduction. Finally, Wolbachia can influence gender determination in its hosts so that more females are successfully born. This results in a reversal in sexual selection, where females must compete for male mates, which has evolutionary implications as it exposes different phenotypes to natural selection.

Entomologists in the early 1900s began to rear Trichogramma spp. for biological control. T. minutum is one of the most commonly found species in Europe and was first mass reared in 1926 on eggs of Sitotroga cerealella. T. minutum has been investigated as a method of biological control of the Choristoneura fumiferana, a major pest of spruce and fir forests.Smith, S.M.; Hubbes, M.; Carrow, J.R. 1986. Factors affecting inundative releases of Trichogramma minutum Ril. against the spruce budworm. J. Appl. Entomol. 101(1):29–39.

Nine species of Trichogramma are produced commercially in insectaries around the world, with 30 countries releasing them. Trichogramma wasps are used for control on numerous crops and plants; these include cotton, sugarcane, vegetables, sugarbeets, orchards, and forests. Some of the pests controlled include cotton bollworm ( Helicoverpa armigera), codling moth ( Cydia pomonella), lightbrown apple moth ( Epiphyas postvittana), and European corn borer ( Ostrinia nubilalis).

Trichogramma species vary in their host specificity. This can lead to nontarget hosts being parasitized. This, in turn, can cause problems by reducing the amount of parasitism of the target host, and depending on the rate of parasitism, nontarget effects could be significant on nontarget host populations. Research is being done on the use of Trichogramma wasps to control populations of spruce bud moth ( Zeiraphera canadensis), which damages white spruce trees.Turgeon, Jean J. "Status of research on the development of management tactics and strategies for the spruce bud moth in white spruce plantations". The Forestry Chronicle. 68 (5): 614–622. doi: 10.5558/tfc68614-5.

Trichogramma began to be seriously used in the 1990s in China. Since then some applications have fallen out of use due to the rise of Bt crop because Bt is also toxic to the parasitoid. Future expansion of Bt in China is expected, and this threatens some uses of Trichogramma, however for some crops/pests it remains the better option and so is expected to continue instead of expanded Bt in those applications. Trichogramma will be especially necessary for resistance management if Bt maize is widely adopted.

In 2021 the National Trust in England embarked on a trial of using Trichogramma evanescens, which parasitises clothes moth eggs, in conjunction with to control common clothes moths, which cause serious damage to carpets, furniture, clothing and other wool and silk objects in historic buildings. The trial was abandoned in 2023; while the microwasps performed well at reducing moth populations in combination with pheromones, they were no better than pheromones alone. It was suspected that the high interiors may not have been suitable and the Trust may continue to use the wasps in smaller stores or where they can be sited close to a known infestation source.